An image forming apparatus having a function of automatically detecting whether an original is a monochromatic original or a color original and making a monochromatic copy or a color copy based on a detection result, has been proposed (see Japanese Laid-Open Patent Publication No. 2006-86629).
When the function is used, in the case of copying a bundle of originals in which a monochromatic original/color original are mixed, the bundle of originals is set on an Auto Document Feeder (ADF) and copying is instructed, a monochromatic copy/color copy is automatically made in accordance with a monochromatic original/color original.
However, when the image forming apparatus erroneously performs monochrome/color detection (color detection), a color copy is made for a monochromatic original or a monochromatic copy is made for a color original.
For example, when an original on which a red seal is put is copied with the use of the function, in a case where the seal is small or the color is light, the ratio of the color part in the original is small, the original is determined as a monochromatic original not as a color original, then a monochromatic copy, instead of a color copy, is made in some cases.
Alternatively, an original having a ground color like coarse paper (straw paper), even in the case of being a monochromatic original, is erroneously determined as a color original in some cases.
In such a case, a user is required to check all the obtained copies to confirm whether the color detection is correctly performed after copying a bundle of originals in which a monochromatic original/color original are mixed.
In a case where color detection has been erroneously performed for even one sheet in the bundle of originals in the above checking, it is necessary to make all the copies again, or pick up an erroneously detected original from the bundle of originals, make a copy again with a correct setting to replace the erroneously copied paper.
When a copy is made using an automatic detection function in this manner, a printing member such as copy paper or a toner is wasted in some cases, and additionally, time for making a copy again is wasted.
Meanwhile, an image forming apparatus having a so-called preview display function, for confirming by displaying a printing image (image data) on a display panel or the like before copying or printing has been proposed. The user, with the use of the preview display function, is able to confirm the printing image before making a copy to cut out the waste of the printing member or the trouble of making a copy again.
By the way, in the image forming apparatus having the preview display function, when an instruction of displaying a preview from a user is received, image data of a firstly scanned original is displayed. It is usual that the image data of the original is sequentially displayed sheet (one image data) by sheet thereafter by an instruction operation of the user.
Accordingly, in the case of scanning a bundle of originals in which 10 pages of monochromatic originals and 10 pages of color originals are repeated, for example, and confirming whether the color detection of originals included in the bundle of originals are performed correctly, it is necessary to operate an instruction button (next display button) and display a preview of image data of the original sheet by sheet sequentially.
In the above-described example, the user needs to operate the instruction button 10 times for displaying the preview of aimed image data of the original in order to confirm whether or not the color detection is performed correctly on the 11th color original, however, such an operation is too troublesome for the user.
Meanwhile, in the case of confirming whether or not the color detection is performed correctly on the original, it is assumed that the user thinks that he/she may make a copy actually after displaying a preview of original image data immediately after (next) a detection result has been switched from color to monochrome or monochrome to color, or original image data before (previous) or after (next) the original image data to confirm that the color detection is performed correctly.